ratchet

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A steplocking device on surgical instruments. As the handles are closed the jaws are also closed and the ratchet holds them in a locked position. The ratchet consists of a notched bar on each handle, the notches facing and overriding when the handles are closed.

• Machinery and Mechanical Devices - ratchet: device that converts continuous motion into intermittent motion, esp. toothed wheel on handle that imparts one-directional motion to tool

This article is about mechanical ratchets. For other uses, see Ratchet (disambiguation).

"Ratchet mechanism" redirects here. For the mechanism of muscle contraction, see Sliding filament model.

A ratchet is a device that allows continuous linear or rotary motion in only one direction while preventing motion in the opposite direction. Because most socket wrenches today use ratcheting handles, the term "ratchet" alone is often used to refer to a ratcheting wrench, and the terms "ratchet" and "socket" are closely associated in many users' minds.

Engraving of the first ratcheting socket wrench and two sockets, invented by J. J. Richardson and patented on June 18, 1863.

Contents 1 Uses 2 Theory of operation 2.1 Backlash 3 See also 4 References 5 External links

Uses

A ratchet lever hoist, usually called a come-along or come-a-long colloquially but most often not in catalogs (probably to avoid real or perceived trademark genericization).

Ratchet mechanisms are used to provide one-way movement in a variety of devices, including:

• Cable ties
• Capstans
• Clocks
• Hoists
• Jacks
• Roller coasters
• Spanners
• Turnstiles
• Winders

Theory of operation

Figure 1: A ratchet featuring gear (1) and pawl (2) mounted on base (3).

Figure 2: A ratchet moving in its "forward" direction.

A ratchet consists of a round gear (see Figure 1) or linear rack with teeth, and a pivoting, springloaded finger called a pawl (or click^[1]) that engages the teeth. The teeth are uniform but asymmetrical, with each tooth having a moderate slope on one edge and a much steeper slope on the other edge.

When the teeth are moving in the unrestricted (i.e., forward) direction (see Figure 2), the pawl easily slides up and over the gently sloped edges of the teeth, with a spring forcing it (often with an audible 'click') into the depression between the teeth as it passes the tip of each tooth. When the teeth move in the opposite (backward) direction, however, the pawl will catch against the steeply sloped edge of the first tooth it encounters, thereby locking it against the tooth and preventing any further motion in that direction.

Backlash

Because the ratchet can only stop backward motion at discrete points (i.e., at tooth boundaries), a ratchet does allow a limited amount of backward motion. This backward motion—which is limited to a maximum distance equal to the spacing between the teeth—is called backlash. In cases where backlash must be minimized, a smooth, toothless ratchet with a high friction surface such as rubber is sometimes used. The pawl bears against the surface at an angle so that any backward motion will cause the pawl to jam against the surface and thus prevent any further backward motion. Since the backward travel distance is primarily a function of the compressibility of the high friction surface, this mechanism can result in significantly reduced backlash.

See also

• Freewheel
• Sprag clutch

References

1. ^ "Know your terminology - Clocks". Hints and Tips. British Horological Institute. http://www.bhi.co.uk/hintsandtips.html. Retrieved 2008-05-15. 

External links

• Silent Ratchet patent (a toothless ratchet) on the USPTO. The patent includes a full description of ratchet technologies, advantages and drawbacks.

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Dansk (Danish)
n. - skralde, skraldeanordning
v. tr. - skralde

idioms:

• ratchet up    forøge, optrappe

Nederlands (Dutch)
pal(rad), van pal voorzien, stapje voor stapje (laten) bewegen

Français (French)
n. - crémaillère, roue à rochet, (Tech, Écon) cliquet
v. tr. - faire augmenter (les prix)

idioms:

• ratchet up    faire augmenter (les prix)

Deutsch (German)
n. - Sperrklinke, Klinkenrad
v. - mit einer Sperrklinke versehen, ein Zahnprofil geben

idioms:

• ratchet up    sich wie unter der Kontrolle eines Zahnkranzes bewegen

Ελληνική (Greek)
n. - (μηχαν.) καστάνια, οδοντωτός τροχός, ανασταλτική οδόντωση
v. - εφοδιάζω/εξοπλίζω με καστάνια

idioms:

• ratchet up    αυξάνω βαθμιαία

Italiano (Italian)
cricchetto, armare di cricchetto

idioms:

• ratchet up    spostare un po' alla volta

Português (Portuguese)
n. - trinco de catraca (m) (Mec.)
v. - rodar na mesma direção

idioms:

• ratchet up    preparar em etapas

Русский (Russian)
храповик, собачка, снабжать храповым механизмом

idioms:

• ratchet up    постепенно повышать

Español (Spanish)
n. - trinquete, retén
v. tr. - subir con trinquete

idioms:

• ratchet up    alzar o subir por efecto de trinquete

Svenska (Swedish)
n. - spärrhake, tjat
v. - spärra, tjata

中文（简体）(Chinese (Simplified))
棘齿

idioms:

• ratchet up    一步步推动

中文（繁體）(Chinese (Traditional))
n. - 棘齒
v. tr. - 棘齒

idioms:

• ratchet up    一步步推動

한국어 (Korean)
n. - 갈쭉톱니바퀴, 바퀴쐐기
v. tr. - 래치트를 달다, 바퀴를 래치트식으로 하다

idioms:

• ratchet up    단계적으로 증가 시키다

日本語 (Japanese)
n. - つめ車装置, つめ車, ラチェット, 追い歯
v. - つめ車で動かす, つめ車を付ける

idioms:

• ratchet up    ラチェットをとり付ける

العربيه (Arabic)
‏(الاسم) السقاطه, ترس, سقاطه (فعل) يزيد تدريجيا‏

עברית (Hebrew)
n. - ‮מערכת שיניים בקצה גלגל או מוט כדי להבטיח תנועה בכיוון אחד בלבד, מחגר‬
v. tr. - ‮התקין מערכת שיניים על מוט או גלגל, נע בשליטת מערכת שיניים‬